The 17055 is used by state and federal Department of Transportation (DOT) agencies to monitor the water content and state (liquid vs. ice) underneath highways. Three rods emanate from the head at right angles. This construction allows the probe to be installed in a highway bed after the highway has been built. To install, a core is drilled into the highway. The probe is "dangled" into the hole by its cable, and then the hole is backfilled.
The "-L" on a product model indicates that the cable length is specified at the time of order.